CI: Add full test support

The patch adds support for running full tests in the local CI
Environment. New features added:

• New target ci-full which runs the full test. This is also the default now
• Renamed the previous target ci-smokeit to ci-smoke
• Unlike previous if the available memory is more than 16G a default of 8G will be used
• Removed some unnecessary debug messages
• Added dummybuf kernel module to the list of modules to be loaded on the VM

The features that can be tested:
make TARGET=<TARGET> TARGET_ARCH=<TARGET_ARCH> CITYPE=full ci
make TARGET=<TARGET> TARGET_ARCH=<TARGET_ARCH> ci is also the same as
above as CITYPE full is the default now

Approved by: lwhsu
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D48015